Utilization of landscape biomass waste as activated carbon to scavenge oxytetracycline: Attraction mechanism, batch and continuous studies

Abstract

Oxytetracycline (OXY) is an antibiotic widely used in the livestock industry and its existence in water can cause antibiotic resistance genes. A treatment process in a continuous mode is required to treat a high volume of OXY wastewater. Hence, an effort was made in this study to adsorb OXY from an aqueous solution (batch and continuous modes) using landscape biomass waste-based activated carbon (LBWAC). This adsorbent was produced via potassium hydroxide (KOH) chemical treatment combined with microwave heating under carbon dioxide, CO2 gas. The resulting LBWAC exhibited 973.21 m2/g of BET surface area, 842.18 m2/g of mesopores surface area, 0.3911 cm3/g of total pore volume, and 2.44 nm of average pore diameter. In a batch study, OXY adsorption uptakes increased whilst OXY percentage removal decreased when OXY starting concentration increased from 25 to 300 mg/L. The highest uptakes of OXY occurred at a solution temperature of 60 °C (228.44 mg/g) and a solution pH of 12 (63.22 mg/g). The adsorption system studied obeyed the Langmuir model and pseudo-second-order in isotherm and kinetic studies, respectively. The obtained Langmuir monolayer capacity, Qm was 344.83 mg/g. Mechanism study revealed that O, H, and N elements in OXY molecules react with O, H, and N elements in functional groups on LBWAC’s surface via hydrogen bonds and vice versa. Parameters acquired in the thermodynamic study described the adsorption process as spontaneous, endothermic, and physisorption-controlled. The continuous bed column study revealed that the breakthrough point (Tb), exhaustion time (Tex), and maximum adsorption uptake (qmax) for the OXY-LBWAC adsorption system can be increased by decreasing the starting inlet concentration, decreasing the inlet flow rate and increasing the bed height. The continuous adsorption data fitted Thomas model the best. The LBWAC had a good potential to be applied in a large-scale operation for OXY wastewater treatment.